During a course of medical treatment, it may be necessary to gain repeat access to specific sites, devices, tissues, or fluids within the body of a patient. This may be effected for the temporary or sustained infusion of various therapeutic agents, the removal and treatment of fluids, the injection of contrast agents, as well as the insertion of various treatment devices such as fiber-optic cameras and light sources, ultrasound probes, and thrombectomy catheters. A number of strategies are currently used to gain such access, including direct vessel cannulation, short and long term catheterization, as well as subcutaneous port and pump implantation.
Direct cannulation of a native or artificial vessel with a needle provides perhaps the least expensive and simplest form of access. However, repeat cannulation of superficial vessels has been shown to result in vessel thrombosis, and in case of hemodialysis graft cannulation, access stenosis and the formation of pseudoaneurisms. A patient's accessible vessels can quickly be eliminated by repeat direct cannulation during the course of some aggressive treatment regimens, limiting treatment options and worsening prognosis.
Short and long term catheters have been used to address the many problems of direct cannulation. These transcutaneous devices are generally flexible cannulae that are inserted percutaneously into the region of interest such as a blood vessel or the peritoneal cavity. Catheters have one or more lumens through which various fluids or devices can pass. While catheters allow repeat access with a reduced risk of vessel thrombosis, they suffer from a number of significant drawbacks. Aside from being unsightly and prone to inadvertent withdrawal, catheters often have complications with infection.
Subcutaneously implanted ports have increasingly been used as an alternative to transcutaneous catheterization. These devices provide a site beneath the skin that can be accessed by special non-coring needles through a percutaneous puncture at the time of treatment. The devices generally comprise a housing that forms a reservoir which communicates with a catheter that leads to the area requiring treatment. A self-sealing septum formed from a high density silicone elastomer spans the top of this reservoir, creating a continuous barrier against the passage of fluids such as blood that are in communication with the port. This septum is punctured by the needle to permit access to the reservoir. Once the needle is withdrawn, the septum closes, restoring the continuous barrier. Ports avoid repeated direct cannulation of a native vessel with a needle. By being completely implanted (that is, requiring no open passage through the skin), ports also avoid many of the infection complications of catheters. In addition, ports are generally better accepted by patients because the ports are less obtrusive, cannot be accidentally withdrawn, and are relatively easy to maintain.
Subcutaneously implanted ports are also used as a means of communicating with other implanted medical devices. For example, implantable infusion pumps that provide a sustained infusion of therapeutic agents into the body of a patient often use one or more integral ports as refilling and flushing sites.
Referring to FIG. 1, an existing implantable access port 10 is shown. The port 10, which is described in detail in U.S. Pat. No. 5,281,199, allows the introduction of various filaments including catheters and needles into the body of a patient without the use of a standard septum. By employing a variety of different valving mechanisms (not shown), the port 10 presumably has broader applications to more rigorous therapies requiring frequent access or high flow, i.e. therapies previously restricted to transcutaneous catheters and direct cannulation. The port 10 includes an access housing 12 which defines a funnel-shaped entrance orifice 14 having a decreasing cross-sectional open area which reduces down to focus area, or entrance opening 16, leading into an internal passageway (not shown) that connects to an exit opening 18. Access housing 12 can be supported subcutaneously by mounting platform 19 having holes 21 for use with sutures or staples.
One significant limitation of the port 10, however, is in the strike area, or the region that the medical professional attempting access must hit with the accessing filament to enter the funnel-shaped entrance orifice 14. A large strike area is critical for simple cannulation and for allowing each insertion wound to heal before that region must be re-cannulated. By nature, to increase the strike area of a generally funnel-shaped entrance orifice 14, one must also increase the funnel's overall size in three dimensions. A dimension of particular importance with ports is height, or depth below the skin. The taller, or deeper, a port, the more tension the port places on the insertion wound of a patient. Increasing the strike area of the funnel-shaped entrance orifice 14, therefore, necessarily increases the height of the port 10 and tension on the insertion wound of a patient.
The funnel-shaped entrance orifice 14 further limits the strike area by providing only a single focal point or entry point for the accessing filament. Because the filament is always focused to the same site, the same tissue proximal to that entry site must be traumatized during each access. Repeat trauma to tissue can lead to devascularization and necrosis, creating a potential site for infection.
Later implantable access ports 10′ and 10″, such as those shown in FIGS. 2 and 3, attempt to overcome the deficiencies of the port 10 of FIG. 1. These later ports 10′ and 10″, which are described in detail in U.S. Pat. No. 5,741,228, each include a housing 12′ having an elongated open guidance channel 14′ and 14″, respectively, communicating with an entrance opening 16′ of the housing. The entrance opening 16′ leads into an internal passageway (not shown) of the housing 12′, which is in turn in fluid communication with a housing exit opening 18′.
The guidance channels 14′ and 14″ both have a substantially constant cross sectional area. Furthermore, in the port 10′ of FIG. 2, the guidance channel 14′ has a generally V-shaped configuration, while in the port 10″ of FIG. 3, the guidance channel 14″ has a generally U-shaped configuration. The channels 14′ and 14″ are for receiving and guiding a filament toward and into the entrance opening 16′. The open guidance channels 14′ and 14″ allow for increases in accessing filament strike area without increasing the overall height of the ports 10′.
What is still desired, however, is an improved needle-receiving port for an implantable device allowing repeated subcutaneous access to a region within the body of a patient. Preferably, the port will provide an even greater filament strike area, yet have a relatively shorter height.